(1) epidermis
Epidermis is the outermost skin, covering the whole body. The thickness varies from location to location, with a general thickness of 0.07mm-2mm. The epidermis can be divided into five layers from outside to inside, namely stratum corneum, transparent layer, granular layer, spinous layer and basal layer. There are no blood vessels in the epidermis, but there are many nerve endings, which can sense external stimuli. Produce a sense of touch, pain and pressure, cold and hot.
1, stratum corneum
The stratum corneum is the outermost layer of epidermis, which protects human body. Can absorb a certain amount of ultraviolet rays. The thickness of stratum corneum has a certain influence on the color of human skin and the absorption capacity of skin. Too thick stratum corneum will make the skin look yellow, dark and dull. The skin has a certain absorption capacity, and the thicker the stratum corneum, the worse the skin absorption capacity. The moisture content of cuticle of epidermis is usually kept between 10%-20%, which makes skin soft, not dry and chapped.
2. Toumian
The transparent layer is located under the stratum corneum, and only the skin with thick stratum corneum such as palm and sole has this layer. The transparent layer consists of 2-3 layers of flat seedless transparent dead cells, which are colorless and transparent and can transmit light.
3. Granular layer
It consists of 2-4 layers of rhombic cells. These cells are almost dead and will soon turn into keratinocytes. Cells contain fine particles, which can refract light and reduce ultraviolet rays from entering the body.
4, spinous layer
It consists of 4-8 layers of polygonal cells with spines, which is the thickest layer in the epidermis. The spinous processes between cells are connected, and interstitial fluid exists in cells, which provides nutrition for cells. There are many sensory nerve endings in the spinous layer, which can sense various external stimuli.
5. Base layer
It is the lowest layer of epidermis, which is connected with dermis in a wave shape and consists of basal cells and melanin.
(basal cell)
Basal cells are cylindrical and arranged in a single layer. They directly absorb nutrients from the capillaries of dermal papilla and have the functions of division, reproduction and repair.
(Melanocyte)
Melanocytes are dendritic and sparsely distributed between basal cells. Some secreted black particles can absorb ultraviolet rays from sunlight and prevent them from being injected into the body to harm deep tissues.
(2), dermis
The dermis is located under the epidermis and is firmly connected with the epidermis in a wavy shape. Its thickness is about 10 times that of epidermis. The dermis can be divided into two layers, the upper layer is the papillary layer and the lower layer is the reticular layer.
1, the papillary layer is located in the superficial dermis, mainly composed of collagen fibers, and contains rich capillary network and sensory nerve endings.
2. The reticular layer is located in the deep dermis and mainly consists of collagen fibers and elastic fibers. The fiber bundles are large, arranged parallel to the skin surface and interwoven into a net. This layer is rich in blood vessels, lymphatic vessels and nerves.
(3), subcutaneous tissue
Subcutaneous tissue is located in the deepest layer of skin, which is a layer of adipose tissue, and its thickness is about 5 times that of dermis. Subcutaneous tissue is mainly composed of a large number of fat cells and loose connective tissue, rich in blood vessels, lymphatic vessels, nerves, sweat glands and deep hair follicles. Subcutaneous fat has the functions of heat preservation, cold protection, external force buffering and skin protection. Fat cells can release energy for human activities after decomposition. The thickness of subcutaneous fat has a great influence on human body shape. Too much fat accumulation will make people look bloated, and too little subcutaneous fat will make people look weak and lack the beauty of lines.
The definition of healthy skin should include
Red is shining.
Smooth, soft and elastic.
Slight moisture content
weakly acidic
Free from defects and diseases.